Process for producing ethylbenzene

ABSTRACT

This ethylbenzene process involves contacting, in an alkylation zone, a first benzene recycle stream and an ethylene feed stream with an alkylation catalyst to form ethylbenzene. In a transalkylation zone, a polyethylbenzene recycle stream and a second benzene recycle stream are contacted with a transalkylation catalyst to form additional ethylbenzene. The effluents are passed into a dividing wall distillation column where a benzene overhead and a benzene side draw are removed and recycled. An ethylbenzene stream product stream is also removed. The remainder, largely polyethylbenzene and tar, is passed to a polyethylbenzene column for separation. The separated polyethylbenzene is recycled to the transalkylation reactor.

FIELD OF THE INVENTION

The invention is directed to a process for producing ethylbenzene usinga dividing wall distillation column.

BACKGROUND OF THE INVENTION

Ethylbenzene is a valuable product that is used mainly for themanufacture of styrene monomer. Most ethylbenzene is produced byalkylation of benzene with ethylene. A byproduct also produced ispolyethylbenzene. Therefore, ethylbenzene production processes containtwo reaction sections, alkylation and transalkylation. Thepolyethylbenzenes produced from minor side reactions are recycled backto the transalkylation section and reacted with benzenes to produce moreethylbenzene. The alkylator and transalkylator effluents undergoseparation operations to separate recycle benzene, ethylbenzene product,recycle polyethylbenzene and by-product streams using distillations.Traditionally three distillation columns are used. The first istypically a benzene column, used to recover excess benzene from thereactor effluents. The benzene column overhead, which is largelybenzene, is typically recycled to the alkylator and transalkylator. Thesecond distillation column is typically an ethylbenzene column used torecover the ethylbenzene product from the benzene column net bottoms.The ethylbenzene product is recovered as overhead, typically the netoverhead, from the ethylbenzene column. The ethylbenzene product may berouted directly as feedstock to a styrene processes unit, or may be sentto storage. The third distillation column is usually a polyethylbenzenecolumn used to recover recycle polyethylbenzene from the ethylbenzenecolumn bottoms stream. Polyethylbenzene is recovered in the overhead ofthe polyethylbenzene column and is typically recycled to thetransalkylator. The high boiling bottoms, flux oil, is usually cooledand sent to storage. Optionally, a fourth column, a light ends column,may be used to remove a small amount of light ends, light non-aromatics,and water from the recycle benzene stream.

The present invention provides an improvement over current process flowschemes by replacing the benzene column and the ethylbenzene column witha single divided wall column. The resulting advantages include a savingsin the HP steam used in the reboilers, a savings in condenser duty, acapital costs savings due to a reduction in equipment count and heatexchanger surface area, and a higher ethylbenzene recovery. Additionaladvantages include a reduction in plot space required, lower flareequipment, and less hydrocarbon inventory which can have a safetyadvantage.

The dividing wall or Petyluk configuration for fractionation columns wasinitially introduced some 50 years ago by Petyluk et al. A recentcommercialization of a fractionation column employing this techniqueprompted more recent investigations as described in the articleappearing at page s14 of a Supplement to The Chemical Engineer, 27 Aug.1992.

The use of dividing wall columns in the separation of hydrocarbons isalso described in the patent literature. For instance, U.S. Pat. No.2,471,134 issued to R. O. Wright describes the use of a dividing wallcolumn in the separation of light hydrocarbons ranging from methane tobutane. U.S. Pat. No. 4,230,533 issued to V. A. Giroux describes acontrol system for a dividing wall column and illustrates the use of theclaimed invention in the separation of aromatics comprising benzene,toluene and orthoxylene.

Using a dividing wall column in the present invention providessignificant advantages over ethylbenzene production processes that donot employ a dividing wall fractionation column, as is shown below.

SUMMARY OF THE INVENTION

An ethylbenzene generation process having a dividing wall fractionationzone has been developed. The process involves contacting, in analkylation zone, a feed stream comprising at least ethylene and a firstbenzene recycle stream comprising at least benzene with an alkylationcatalyst under alkylation conditions to convert at least a portion ofthe ethylene and benzene into ethylbenzene and form an alkylation zoneeffluent comprising benzene and ethylbenzene. Also, in a transalkylationzone, a polyethylbenzene recycle stream comprising at leastpolyethylbenzene and a second benzene recycle stream comprising at leastbenzene are contacted with a transalkylation catalyst undertransalkylation conditions to convert at least a portion of thepolyethylbenzene and benzene into ethylbenzene and form atransalkylation zone effluent comprising benzene and ethylbenzene. Thealkylation zone effluent and the transalkylation zone effluent arepassed into a dividing wall fractionation column which is operated atfractionation conditions. The dividing wall fractionation column isdivided into at least a first and a second parallel fractionation zoneby a dividing wall, with the first and the second fractionation zoneseach having an upper and a lower end located within the fractionationcolumn, with the first and second fractionation zones being in opencommunication at their upper ends with an undivided upper section of thefractionation column and in open communication at their lower ends withan undivided lower section of the fractionation column.

The two reactor effluent streams enter the column at one or moreintermediate points of the first fractionation zone.

A stream comprising ethylbenzene is removed from an intermediate pointof the second fractionation zone of the dividing wall fractionationcolumn. A first benzene recycle stream is removed from a first end ofthe dividing wall fractionation column. The second benzene recyclestream is removed from an intermediate point of the second fractionationzone of the dividing wall fractionation column located between theethylbenzene stream and the first end of the dividing wall fractionationcolumn, and a polyethylbenzene stream is removed from a second end ofthe dividing wall fractionation column. The net polyethylbenzene streamis passed to a polyethylbenzene fractionation column to separate thepolyethylbenzene recycle stream from a flux oil stream.

BRIEF DESCRIPTION OF THE DRAWING

The FIGURE is a schematic illustration of one embodiment of the presentinvention. The Figure does not show a number of details for the processarrangement such as pumps, compressors, valves, stabilizers and recyclelines which are well known to those skilled in the art.

DETAILED DESCRIPTION OF THE INVENTION

Referring to the FIGURE, the process of the invention requires tworeactors, an alkylation reactor 2, or alkylator, and a transalkylationreactor 4, or transalkylator. Ethylene feedstock 6 and an excess ofbenzene 8 are introduced to alkylator 2. A typical ethylene feedstockmay contain polymer grade ethylene (99.9 vol-% min.) acetylene (10 ppmvol-% max.), acetylene (1 ppm vol.-% max.), dienes (1 ppm vol.-% max),propylene (25 ppm vol-% max.), and C3 and heavier components (100 ppmvol.-% max). A typical benzene feedstock may contain benzene (99.9 wt.-%min.) and toluene (0.05 wt.-% min). Alkylation reactors may be operatedin the vapor phase, liquid-phase or mixed-phase. It is preferred tooperate the alkylation reactor in the liquid phase. At the lowertemperatures of the liquid phase operation, xylene impurities are notproduced and an ethylbenzene product of superior quality is produced. Inone embodiment, the temperature of the alkylation reactor is selectedfrom the range of 100° C. to 310° C. (212 to 590° F.) and the pressureis selected from the range of 800 to 5100 kPa (116 to 740 psig). In amore specific embodiment the temperature is in the range of 150 to 280°C. (303 to 536° F.) or 120 to 280° C. (248 to 536° C.) and the pressureis in the range of from about 1000 to 3900 kPa (145 to 570 psia).Alkylation reactor 2 contains an effective amount of alkylationcatalyst. Suitable alkylation catalysts include solid acid catalysts andpreferably a solid oxide zeolite. Examples are zeolite beta, zeolite X,zeolite Y, mordenite, faujasite, zeolite omega,MCM-22,MCM-36,MCM-49,MCM-56 and UZM-8.Alkylation reactors, operatingconditions and catalysts are known in the art and not further discussedhere.

In alkylation reactor 2, the benzene is alkylated with the ethylene toform ethylbenzene. Some polyethylbenzenes, which are mainly di- andtri-substituted ethylbenzenes, are also formed. Benzene is fed to thealkylator in excess so that virtually all the ethylene is reacted.Therefore, alkylation reactor effluent 10 contains primarily benzene,ethylbenzene and polyethylbenzenes.

Transalkylation reactor 4 is used to transalkylate the polyethylbenzeneproduced in the alkylation reactor and recycled in line 43 with benzenerecycled in line 20 to form additional ethylbenzene. Suitable conditionsand catalysts may be the same as described for the alkylation reactor.In one embodiment, the temperature is selected from the range of 170° C.to 270° C. (228 to 518° F.) and the pressure is selected from the rangeof 800 to 5100 kPa (116 to 740 psia). The transalkylation effluent 12from transalkylation reactor 4 contains primarily benzene, ethylbenzeneand polyethylbenzene. Transalkylation effluent 12, for example, maycontain from 30 to 70 wt.-% benzene, 10 to 50 wt.-% ethylbenzene, 5 to30 wt.-% polyethylbenzene include solid acid catalysts and preferably asolid oxide zeolite. Examples are zeolite X, zeolite Y, mordenite,faujasite, zeolite omega, MCM-22,MCM-36,MCM-49,MCM-56 andUZM-8.Transalkylation reactors, operating conditions, and catalysts areknown in the art and not further discussed here.

Both alkylation effluent 10 and transalkylation effluent 12 areintroduced to ethylbenzene/benzene dividing wall distillation column 14either as a combined stream or separately. Within the dividing walldistillation column are two parallel fractionation zones. A firstfractionation zone occupies a large portion of the left-hand side of themid-section of the distillation column. Note that the terms “left-hand”and “right-hand” are used herein as relative to the drawings. In actualpractice the placement of the zones as to the left side or the rightside of the column is not critical. This first fractionation zone isseparated from a parallel second fractionation zone occupying the otherhalf of the column cross section by a substantially fluid tight verticalwall 16. The vertical wall is not necessarily centered in the column andthe two fractionation zones may differ in cross sectional area or shape.The vertical wall divides the vertical portion of the column into twoparallel fractionation zones. The two zones are isolated from each otherfor the height of this wall, but communicate at both the top and bottomends of the column. There is no direct vapor or liquid flow between thetwo fractionation zones through the dividing wall, but the upper end ofthe fractionation zone is open to the internal volume of thedistillation column, thereby containing an undivided fractionation zonepreferably having additional trays. Liquid may pass under the dividingwall at the bottom of the two fractionation sections although vapor flowis preferably restricted or controlled. Thus, vapor and liquid canfreely move around the wall between the two portions of the column.

During operation, the components of both effluents are separated in thefirst fractionation zone with the more volatile compounds moving upwardout of the left-hand first fractionation zone and emerging into theundivided upper portion of the distillation column. As with the firstfractionation zone, the upper end of the right-hand second zone is inopen communication with the upper section of the distillation columnwhich may optionally contain additional fractionation trays extendingacross the entire column cross section.

The components of the effluent will separate according to boiling pointor relative volatilities, which is the main factor in determining theirbehavior in the distillation column. The component having a relativelylow boiling point is the benzene from each of the effluents. Themid-range boiling component is the desired product, ethylbenzene. Thecomponents having relatively high boiling points are thepolyethylbenzenes and any flux oil.

The transalkylation effluent 12 and the alkylation effluent 10 areintroduced into a first vertical fractionation zone occupying a largeportion of the left-hand side of the midsection of the distillationcolumn. The effluents may be combined before being introduced, butadvantages may be realized by introducing the effluents at differentheights along the dividing wall distillation column. For example, thetransalkylation reactor effluent may contain a higher concentration ofpolyethylbenzene and therefore it may be advantageous to introduce thetransalkylation reactor effluent at a relatively lower height along thecolumn as compared to the transalkylation reactor effluent. In oneembodiment, the alkylation zone effluent is introduced into the dividingwall fractionation column at an intermediate height which is in betweenthe height at which the transalkylation zone effluent is introduced andthe first end of the of the column where the overhead is withdrawn.

The benzene present in the effluents is driven upward in the firstfractionation zone and enter the top section of the column where it isremoved in overhead 18 and side draw 20. In one embodiment, the dividingwall column is operated so that the overhead is at a temperature rangingfrom about 88° C. to about 104° C. (190 to 220° F.) and a pressureranging from about 103 to 241 kPa (15 to 35 psia). In a more specificembodiment, the dividing wall column is operated so that the overhead isat a temperature of about 98° C. (208° F.) and a pressure of about 172kPa (25 psia). Benzene in overhead 18 is removed from the top of thedividing wall column and passed through an overhead condenser 38 to formliquid delivered to receiver 22. Steam 24 may be removed from receiver22 for applications such as use in a styrene process. Receiver 22 mayalso have vent stream 21. A liquid phase stream of benzene 26 is removedfrom the receiver and divided into a first portion 28 which is returnedto the top of the dividing wall fractionation column as reflux and asecond portion 8 which is recycled to the alkylation reactor 2. Benzenemay also be removed from dividing wall column in stream 20 which is aside draw. Benzene stream 20 may be recycled to transalkylation reactor4. Two benzene stream may be withdrawn from the benzene column becausethe catalysts typically used in the alkylation reactor can tolerate somewater present during the alkylation reaction, but the catalyststypically used in the transalkylation reactor are less tolerant ofwater. Therefore, the overhead contains benzene which may be saturatedwith water and is appropriate for the alkylation reactor, while the sidedraw contains dry or semi-dry benzene which is appropriate for thetransalkylation reactor. As used herein the term “rich” is intended toindicate a concentration of the indicated compound or class of compoundsgreater than 50 and preferably greater than 75 mol percent.

The bottom of the dividing wall fractionation column 14 also comprisesan undivided fractionation zone. This zone can receive liquid drainingfrom both the first and second fractionation zones. This liquid issubjected to distillation which drives the ethylbenzene upwards as vaporwhile concentrating the less volatile polyethylbenzene and flux oil intoa bottoms liquid 34 that is removed from dividing wall fractionationcolumn 14. This separation is effected through the use of a reboiler 36providing vapor to the bottom undivided fractionation zone. The productethylbenzene stream 32 is withdrawn from the dividing wall fractionationcolumn in a side draw from the right-hand side fractionation zone. A netportion of bottoms stream 34 is passed to polyethylbenzene separationcolumn 40.

In a more specific embodiment of the invention, the undivided bottomsection of the dividing wall fractionation column is depicted asseparated from the two parallel fractionation zones by a gas flowcontrol or gas trap-out tray located just below the bottom of the wall.A slight gap at this point allows horizontal liquid flow between theparallel fractionation zones. This tray may have liquid sealedperforations, or downcorners, allowing the normal downward flow ofliquid, but its structure is such that the upward flow of vapor is atleast greatly restricted. The tray may totally block the upward vaporflow. The use of this tray may provide a means to positively control thedivision of the upward gas flow between the two fractionation zones,which is a prime means of controlling performance of the two zones. Thetotal vapor flow is, therefore, preferably routed from the column via aline and split between two separate lines which feed the vapor to thebottom of the two parallel fractionation zones separately. The gas flowmay be controlled by one or more flow control valves or by adjusting therelative liquid levels in the bottom of the two zones. This is describedin some detail in U.S. Pat. No. 4,230,533.

A net portion of bottoms stream 34 containing primarily polyethylbenzeneis passed to polyethylbenzene column 40 for the separation ofpolyethylbenzene into polyethylbenzene column overhead 42, and flux oilinto polyethylbenzene column bottoms 44. In one embodiment the column isoperated so that the overhead temperature is from about 121° C. to about138° C. (250 to 280° F.) and the pressure is from about 21 to about 23kPa (3.0 to 3.3 psia). In a more specific embodiment the column isoperated so that the overhead is at about 130° C. (266° F.) and 22 kPa(3.2 psia). Polyethylbenzene column overhead 42 containing primarilypolyethylbenzene passed through receiver 46 and a portion may bereturned to the top portion of polyethylbenzene column 40 as reflux. Theremainder of the stream, net polyethylbenzene column overhead 43, isrecycled to transalkylation reactor 4.

In another embodiment of the invention, there may be a need to generatelow pressure steam, usually for use elsewhere at the plant site. In thisembodiment, cooling water in optional line 19 may be heat exchanged withdividing wall overhead stream 18, second benzene recycle stream 20 usingoptional heat exchanger 21, and ethylbenzene stream 32 using optionalheat exchanger 23 to form low pressure steam in optional line 29. Ifless steam is required, fewer heat exchange operations with fewerstreams are employed. For example, water in line 19 may be exchangedonly with overhead 18 to generate the steam; only with second benzenerecycle stream 20 using optional heat exchanger 21 to generate lowpressure steam; or only with ethylbenzene stream 32 using optional heatexchanger 23 to form low pressure steam. Any combination of heatexchange operations may be employed depending upon the application andthe requirements for low pressure steam.

The theoretical modeling results shown in the Table indicate that theseparation performed in the present invention would compare favorably tothat achieved using a conventional scheme employing a benzene columnfollowed by an ethylbenzene column. The representative comparison of theseparations as shown in FIG. 1 The data is based solely upon engineeringdesign calculations and indicates that two conventional fractionationcolumns (the benzene column and the ethylbenzene column) could bereplaced with the dividing wall column of the present invention toprovide significant benefits and costs savings. For example, thedividing wall column of the present invention requires a total reboilingduty of 20.4 MW (69.7 MMBTU/hr) versus 36.5 MW (124.7 MMBTU/hr) or 28 MW(96 MMBTU/hr) for the two conventional columns, depending upon thepressures of the conventional benzene column. The dividing wall columnrequires a total condenser duty of −41.7 MW (−141.6 MMBTU/hr) versus−46.6 MW (−159 MMBTU/hr) for the two conventional columns. At the sametime, the dividing wall column requires a total number of stages of 56,versus 72 or 62 stages for the conventional columns, depending upon thepressure of the benzene column. Finally, the data shows there is a smallincrease in ethylbenzene recovery which translates into a smaller lossof ethylbenzene product. Therefore, the present invention, through theuse of the dividing wall column reduces the capital costs as to thenumber of trays and lower equipment count as well as the utility costsas compared to a conventional fractionation column.

In a conventional process the benzene column may be operated at anoverhead pressure of 672 kPa (97.5 psia) so that the condenser can beused to produce an LP stream that can be used elsewhere at the plantsite, and the first simulation in the example was modeled at this higheroverhead pressure in the benzene column. However, the dividing wallcolumn was modeled in the example at an overhead pressure of 172 kPa (25psia) so that the column could be reboiled with high pressure steam. Thelower pressure gives the dividing wall column of the present inventiontwo additional advantages over the conventional two column sequence withthe benzene column being operated at a higher pressure. First, the feedstreams will flash to a higher vapor fraction which will in turn, reducethe amount of vapor that must be generated in the column. Second, therelative volatilities in the column will increase, leading to an easierseparation. For a complete comparison a second simulation was modeledwith the benzene column of the conventional two column scheme operatingat an overhead pressure of 172 kPa (25 psia). In the Table, “Case 1”signifies the conventional benzene column followed by an ethylbenzenecolumn where the benzene column is operated at an overhead pressure of672 kPa (97.5 psia), and “Case 2” signifies the conventional benzenecolumn followed by an ethylbenzene column where the benzene column isoperated at an overhead pressure of 172 kPa (25 psia). As the datademonstrates, regardless of the operating pressure of the benzenecolumn, the divided wall column of the present invention providesadvantages and benefits.

TABLE DWC Savings Compared Compared Benzene Column EB Column Total to toCase 1 Case 2 Case 1 Case 2 Case 1 Case 2 DWC Case 1 Case 2 OverheadPkPa  672(97.5) 172(25)   175(25.4)  175(25.4) — — 172(25)  (psia)Overhead Toc 156(314)  98(208) 158(316) 158(316) — —  98(208) (deg. F.)Cond QMW  −35.1(−119.8) −36.0(−123)  −11.4(−39)   −10.5(−36)   46.5(−158.8) −46.5(−159)   −41.5(−141.6) 10.8% 10.9% (MMBTU/hr) BottomsToc 236(457) 174(346) 226(439) 226(439) — — 223(433) (deg. F.) Reb QMW25.5(87.2) 14.6(50)   11.0(37.5) 13.4(46)    36.5(124.7) 28.1(96)  20.4(69.7) 44.1% 27.4% (MMBTU/hr) Total # Stages 38 30 34 32 72 62 56Column Diameter  4.7(15.5) 5.2(17)  3.4(11)  3.4(11)  — — 5.8(19)  M(ft) (Stg 1-15) (Stg 1-15)  (Stgs 1-44)   5.0(16.5) 4.0(13)  4.6(15) (Stg 16-38) (Stg 16-30) (Stg 45-56) EB in Benzene 2.5 2.5 2.5 to TAReactor (wt. %) Benzene in EB 126 126 86 Product (ppmw) DEB in EB 50 5050 Product (ppmw) EB in bottoms 2 2 1.6 (wt. %) EB Recovery 96.6 96.596.8

1. An ethylbenzene generation process using a dividing wallfractionation zone, said process comprising: contacting, in analkylation zone, at least ethylene, benzene, and a first benzene recyclestream comprising at least benzene with an alkylation catalyst underalkylation conditions to convert at least a portion of the ethylene andbenzene into ethylbenzene and form an alkylation zone effluentcomprising benzene and ethylbenzene; contacting, in a transalkylationzone, a polyethylbenzene recycle stream comprising at leastpolyethylbenzene and a second benzene recycle stream comprising at leastbenzene with a transalkylation catalyst under transalkylation conditionsto convert at least a portion of the polyethylbenzene and benzene intoethylbenzene and form a transalkylation zone effluent comprising benzeneand ethylbenzene; passing the alkylation zone effluent and thetransalkylation zone effluent into a dividing wall fractionation columnoperated at fractionation conditions and divided into at least a firstand a second parallel fractionation zone by a dividing wall, with thefirst and the second fractionation zones each having an upper and alower end located within the fractionation column, with the first andsecond fractionation zones being in open communication at their upperends with an undivided upper section of the fractionation column and inopen communication at their lower ends with an undivided lower sectionof the fractionation column, and with the alkylation zone effluent andthe transalkylation zone effluent entering the column at one or moreintermediate points of the first fractionation zone, and wherein thealkylation zone effluent is introduced into the dividing wallfractionation column at an intermediate height of the dividing wallfractionation column which is in between the height at which thetransalkylation zone effluent is introduced and the first end of thedividing wall fractionation column; removing a stream comprisingethylbenzene from an intermediate point of the second fractionation zoneof the dividing wall fractionation column; removing the first benzenerecycle stream from a first end of the dividing wall fractionationcolumn wherein the dividing wall fractionation column is operated sothat the first benzene recycle stream removed from the first end of thedividing wall fractionation column is at a pressure ranging from 103 to241 kPa (15 to 35 psia) and a temperature ranging from about 88 to 104°C. (190 to 220° F.); removing the second benzene recycle stream from anintermediate point of the second fractionation zone of the dividing wallfractionation column; removing a polyethylbenzene-rich stream from asecond end of the dividing wall fractionation column; passing thepolyethylbenzene-rich stream to a polyethylbenzene fractionation columnto separate the polyethylbenzene recycle stream from a flux oil-richstream.
 2. The process of claim 1 wherein the alkylation zone isoperated at a pressure in the range of from about 800 to about 5100 kPa(116 to 740 psia) and a temperature in the range of 100 to 310° C. (212to 590° F.).
 3. The process of claim 1 wherein the transalkylation zoneis operated at a pressure in the range of 800 to 5100 kPa (116 to 740psia) and a temperature in the range of 170 to 270° C. (338 to 518° F.).4. The process of claim 1 wherein the polyethylbenzene column isoperated so that the polyethylbenzene recycle stream is at a pressureranging from 21 to 23 kPa (3.0 to 3.3 psia) and a temperature rangingfrom about 121 to 138° C. (250 to 280° F.).
 5. The process of claim 1further comprising heat exchanging a cooling water stream with a streamselected from the group consisting of: a. the first benzene recyclestream removed from the first end of the dividing wall fractionationcolumn, b. the second benzene recycle stream from an intermediate pointof the second fractionation zone of the dividing wall fractionationcolumn, c. the stream comprising ethylbenzene removed from anintermediate point of the second fractionation zone of the dividing wallfractionation column, and d. any combination thereof to generate a steamstream.
 6. The process of claim 1 further comprising passing the streamcomprising ethylbenzene from an intermediate point of the secondfractionation zone of the dividing wall fractionation column to aprocess for generating styrene monomer.
 7. An ethylbenzene generationprocess using a dividing wall fractionation zone, said processcomprising: contacting, in an alkylation zone, at least ethylene,benzene, and a first benzene recycle stream comprising at least benzenewith an alkylation catalyst under alkylation conditions to convert atleast a portion of the ethylene and benzene into ethylbenzene and forman alkylation zone effluent comprising benzene and ethylbenzene;contacting, in a transalkylation zone, a polyethylbenzene recycle streamcomprising at least polyethylbenzene and a second benzene recycle streamcomprising at least benzene with a transalkylation catalyst undertransalkylation conditions to convert at least a portion of thepolyethylbenzene and benzene into ethylbenzene and form atransalkylation zone effluent comprising benzene and ethylbenzene;passing the alkylation zone effluent and the transalkylation zoneeffluent into a dividing wall fractionation column operated atfractionation conditions and divided into at least a first and a secondparallel fractionation zone by a dividing wall, with the first and thesecond fractionation zones each having an upper and a lower end locatedwithin the fractionation column, with the first and second fractionationzones being in open communication at their upper ends with an undividedupper section of the fractionation column and in open communication attheir lower ends with an undivided lower section of the fractionationcolumn, and with the alkylation zone effluent and the transalkylationzone effluent entering the column at intermediate points of the firstfractionation zone, wherein the alkylation zone effluent is introducedinto the dividing wall fractionation column at an intermediate height ofthe dividing wall fractionation column which is in between the height atwhich the transalkylation zone effluent is introduced and a first end ofthe dividing wall fractionation column; removing a stream comprisingethylbenzene from an intermediate point of the second fractionation zoneof the dividing wall fractionation column; removing the first benzenerecycle stream from the first end of the dividing wall fractionationcolumn; removing the second benzene recycle stream from an intermediatepoint of the second fractionation zone of the dividing wallfractionation column; removing a polyethylbenzene-rich stream from asecond end of the dividing wall fractionation column; and passing thepolyethylbenzene-rich stream to a polyethylbenzene fractionation columnto separate the polyethylbenzene recycle stream from a flux oil-richstream.
 8. The process of claim 7 wherein the alkylation zone isoperated at a pressure in the range of from about 800 to about 5100 kPa(116 to 740 psia) and a temperature in the range of 100 to 310° C. (212to 590° F.).
 9. The process of claim 7 wherein the transalkylation zoneis operated at a pressure in the range of 800 to 5100 kPa (116 to 740psia) and a temperature in the range of 170 to 270° C. (338 to 518° F.).10. The process of claim 7 wherein the dividing wall fractionationcolumn is operated so that the first benzene recycle stream removed froma first end of the dividing wall fractionation column is at a pressureranging from 103 to 241 kPa (15 to 35 psia) and a temperature rangingfrom about 88 to 104° C. (190 to 220° F.).
 11. The process of claim 7wherein the polyethylbenzene column is operated so that thepolyethylbenzene recycle stream is at a pressure ranging from 21 to 23kPa (3.0 to 3.3 psia) and a temperature ranging from about 121 to 138°C. (250 to 280° F.).
 12. The process of claim 7 further comprising heatexchanging a cooling water stream with a stream selected from the groupconsisting of: a. the first benzene recycle stream removed from thefirst end of the dividing wall fractionation column, b. the secondbenzene recycle stream from an intermediate point of the secondfractionation zone of the dividing wall fractionation column, c. thestream comprising ethylbenzene removed from an intermediate point of thesecond fractionation zone of the dividing wall fractionation column, andd. any combination thereof to generate a steam stream.
 13. The processof claim 7 wherein the alkylation zone effluent is introduced into thedividing wall fractionation column at an intermediate height of thedividing wall fractionation column which is in between the height atwhich the transalkylation zone effluent is introduced and the first endof the dividing wall fractionation column.
 14. The process of claim 7further comprising passing the stream comprising ethylbenzene from anintermediate point of the second fractionation zone of the dividing wallfractionation column to a process for generating styrene monomer.